Fungal disease found in Aroostook potato field

The disease late blight has been found in Presque Isle, potato industry experts said.

Late blight is a fungal disease that affects potatoes and tomatoes, and can cause widespread crop destruction, according to the University of Maine Cooperative Extension.

A sample from a commercial potato field in Presque Isle showed evidence of the disease, reported Extension specialists in their weekly Potato Pest Report on Aug. 9.

The disease devastated crops in 2009 and, in the wake of stellar growing years in 2021 and 22, growers don’t need bad news like last year’s constantly wet season. Late blight can be remedied by preemptive spraying, and the Extension is urging growers to adhere to a schedule to preserve the crop.

The pest report is issued weekly throughout the growing season by a specialist team, including Sean McAuley, scientific technician, James Dill, pest management specialist; I. Kutay Ozturk, potato plant pathologist; and Griffin Dill, integrated pest management professional.

“Weather conditions in most potato-growing regions in Maine are conducive to disease formation,” the team said in the report.  “It is advised to maintain scouting efforts and continue with the recommended spray schedules.”

Hurricane Beryl in early July didn’t affect Maine much, but its conditions caused late blight in Canada and were expected to bring disease-favorable weather to Maine.

Late blight is caused by Phytophthora infestans, a fungus-like organism that can infect potatoes and plant leaves. It causes discolored spots on leaves and in potatoes, according to the Extension publication “ Potato Late Blight .”

Spores can travel through the air, but the organism can’t live in soil or dead plants, and hot, dry weather and spraying can keep the disease at bay. Thorough killing of potato plants is recommended before harvest, the report stated.

The Maine Organic Farmers and Gardeners Association also reported the blight found in Presque Isle. The specific strain of the organism, and how widespread it may be, is not known, according to a newsletter from crops specialist Caleb Goossen. But potato and tomato growers should apply preventive measures like fungicides as per directions, and removing lower tomato leaves so air can get to the plants.

Cool, moist weather is ideal for blight formation, according to an Extension bulletin . An outbreak in 2009, when long periods of rainy, humid weather hit Maine, severely affected tomatoes and potatoes. Late blight is also blamed for the 1840s Irish potato famine, the bulletin said.

Since remnants of tropical storm Debby were evident over the weekend, specialists advised growers to be vigilant. Some Aroostook County areas were on preventative spray schedules of every six or seven days for late blight, but as of Friday, all areas should spray every five days, the specialists said.

The organism that causes late blight does not overwinter in the soil in Aroostook County’s climate, according to the Extension.